The control mechanism operating in the in vitro replication of phi chi RFI DNA will be continued. The precise role played by the phi chi induced A protein as well as the Phi chi A* protein will be examined. The further disection of the adenovirus DNA replication system will be continued. This system has now been divided into two major reactions; one involves the elongation of primed Ad DNA and the second involving the initiation of Adeno DNA synthesis. The influence of various carcinogens on each of these DNA replication systems will be carried out.